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ABV and Back Sweetening

Koryr6

NewBee
Registered Member
Nov 10, 2010
2
0
0
Hi all. I have searched through the forums and around the internet and haven’t been able to find a specific answer to my question.

I have made a couple of step by step recipes and am to the point that I would like to attempt a “do it from scratch” approach. I like the idea of taking a mead dry and then back sweetening to a desired level for somewhat reliable repeatability (is that a word? ;D).

My question is about ABV and how it is impacted by back sweetening
If for example, I was shooting for a 14% ABV, fermented to dry at .998, and back sweeten to 1.020 where should my starting gravity be?

According to the calculator, if I used it correctly. (I love this thing by the way)
Example 1: S.G of 1.127 taken to F.G of 1.020 = roughly 14% ABV​
Example 2: S.G of 1.105 taken to F.G of .998 = roughly 14% ABV​


Sooo which, if either, is correct? Should there be a 3rd example that somehow uses a measured amount of sweetened liquid at a known gravity to account for how the must is diluted?

Thanks in advance for info on this topic.
 

kudapucat

NewBee
Registered Member
Dec 2, 2010
2,383
10
0
Bundoora, Melbourne, Australia
ABV + alcohol by volume

It is approximated by SG - FG * 135 (135 is the constant used for mead, it's lower for lower alcohols like beer)

so 0.107 * 135 = 14.5%

You are correct. It is only the difference in gravity that matters (with this approximation), not where on the scale the difference appears.

When you backsweeten you are not adding any alcohol. but you are adding volume.

So simply if you have 14.5% alcohol in 1 gallon, then you have 0.145 gallons of pure alcohol in there.
If you add a pint of honey (That's a large amount, but it makes the math easier for me because SAE is not my first language) then you end up with 1.125 gallons with 0.145 gallons alcohol in it.
so 0.145/1.125 = 12.9 % ABV

Does that make sense?

the forumula you use is:


(original volume X ABV)
new ABV = __________________________________________

(original volume) + (backsweetened honey volume)


Of course, if you have live yeast in your must when you backsweeten, it will start to eat the honey, and FIIK what the ABV will be after that.
 

Koryr6

NewBee
Registered Member
Nov 10, 2010
2
0
0
That makes perfect sense! Thank you very much for the information and for the super quick response.
 

kudapucat

NewBee
Registered Member
Dec 2, 2010
2,383
10
0
Bundoora, Melbourne, Australia
Thanks medsen, I don't have a gut feel for the quantities. That's very helpful.
So the math behind what median said is this:

0.55 pound = 250 grams
Honey has an SG of about 1.4
250/1.4 = 180 mililitres
Or about a third of a pint. Or 6 FlOz (I think)
That's why with a sane amount of honey, as Medsen has suggested, the ABV changes by about a third as much.
 

kudapucat

NewBee
Registered Member
Dec 2, 2010
2,383
10
0
Bundoora, Melbourne, Australia
SG is defined as kg per litre at 20C. 1 Litre of water at 20 C weighs 1kg
(for most measuring tools - SI units would be at 25 C for lab conditions)

So it can be said that your gallon of water has an sg of 1.000 (at 20C)
1 gallon = 3.8 litres (approx)
so your gallon of water weighs 3.8kg

3 pounds = 1.36kg (approx)
honey has an SG of about 1.4 (1.4 kg/litre)
so your 3 pounds will take up almost a litre (1.36/1.4)

When you add you honey you will therefore have 3.8 + 1.0 = 4.8 litres of must

3.8kg + 1.36kg = 5.15kg / 4.8 litres = 1.07 kg/l

making your SG 1.07

Now substitue any other values to alter the calculation so you get a SG to your liking.